Volume-control system



June 4, 1929 l o. B. HANSON ET AL j h 1,715,415

VOLUME CoNTRoL-sYsTEM Y l I Filed D ec. 19, 1925 ATTORNEY Patented 'June 4, 1929.

UNITEDA STATESv PATENT OFFICE.

OSCAR B. HANSON, OF ROSELLE, GEORGE CRISSON, OF ORANGE, AND FREDERICK W. MCKOWN, OF ENGLEWOOD, NEW JERSEY, ASSIGNORS T AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

VOLME-CONTROL SYSTEM.

' application med December 19, 1925. serial No. 76,548.

This invention relates'to volume range control systems, and particularly to a system adapted to compress the volume range to be f transmitted over or through the medium connecting the parts of the system and to expand it at the receiving points of the system, controlling the degree of expansion in accordance with` the particular requirements of each receiving station. y

In the broadcast system in which a plurality of radio broadcast stations are connected by a transmission circuit with a transmitting station to eect the broadcasting of the same program from all ot' said broadcast stations, it is desirable to compress the volume range of the output of the transmitteramplifier at the transmitting station in order to bring such volume range within the range that the transmitting medium, such asa wire line, is capable of transmitting, and to expand the volume range at the receiving stations, so as to bring the music, speech or whatever constitutes the' transmitted material, back to its volume range before compression took 25 vplace at the transmitting station. A method and means for simultaneously controlling the compression and expansion at the transmitting and receiving stations, respectively, are

disclosed in the patent to A. B. Clark, No.

1,565,548, that issued on December 15, 1925.

Experience has shown that where several radio broadcast stations are connected with the transmission line, it has been found desirable to supply each of the dierent stations with different volume ranges, depending upon the conditions prevailing in the zone in which each station broadcasts.

This invention resides in a method and'l means for compressing the volume range 40 of the output of the transmitting station before impressing it upon the transmission line and expanding the volume range at radio broadcast statlons or at a loud-speaker installation, the degree of expansion depending upon the particular requirements of each station.

This invention will be clearly understood from the following description when read in connection with the attached drawing, of

0 which Figure 1 shows schematically an arrangement for carrying out the invention,

- Fig. 2 shows in greater detail a circuit for vcarrying out the invention7 and Figs. 2a and .2b illustrate the arrangements for compress- -or speech, or other sounds, are picked up and impressed upon a transmitter-amplier such as 1s representedby 2. The output of this amplifier, which will, for the purpose of illustrating this invention, be assumed to have a volume range from 15 TU to -45 TU, is c`on nected with a compressor 3 which has a range of 45 TU. This compressor is connected with the input side ofthe amplifier 4 which has its output side connected with the line L1. This line may have one or more repeaters such as is represented by 5, and may be connected at various points throughout its length with a 70 plurality of radio broadcast stations 1, 2 and 3, and with a loud speaker system designated No. 4. The radio station N o. l is'connected f directly with the line L1, but the other radio stations and the loud speaker system have expanders 6, 7 and 8 inserted between the station or system andthe'points of connection 4with the line. Bridged across the output of the transmitter-amplifier 2 is a comp1essor'9 wlviich is connected with the volume indicator Let it be assumed that a symphony concert isbeing picked' -up by the transmitter 1 for broadcasting from the radio stations Nos. 1 to 3, and from the loud speaker system No. 4. Let it also be assumed that the Volume at the output of the transmitter-amplifier 2 has a range vVarying from +15 yTU to -45 TU. Owing to the presence of the compressor 3, the output volume of the amplifier 2 Will be compressed within the range of SOand -45 TU. This volume is impressedy upon the amplier 4 having the gain of 45 -TU so that the output volume of this: ampliier has a range extending from zero to +15 TU, which is a range of volume and which represents the levels adapted for transmission over the long lines to the radio broadcast stations and the loud speaker system.v Since the radio station 1 desires a volume range of only 100 15 TU, it'would be directly connected with the line L1 inasmuch as such is the volume range transmitted by the said line. If a station such as No. 2 desires a greater range of volume, it is necessary only to use an expander of the proper size, which, in the case i1- ,4o v ing that the volume applied to the input side lustrated, isv that giving a volume rangeof 30 TU, that is-to say, from 15 TU to 15TU.

Another station suchas N o. 3 desiring a still greater range lwould have a 30 TU expander inserted lbetv'veen the station and the line L1.

l While it is probable that the, volume'range represented by station No. 3 ,would be the maximum' required by a radio station.it may be desirable to -urther expand the volume for the purpose of reproducing the concert ina hall at a distant point by means of a loud'l speaker system, which would expand the music tothe original volume range possessed by, it at the hall Where the concert was being performed. In such an event, a. 45 TU ex'- pander Would expand the volume range of the line from +15 TU to -45 TU, which would be 4the volume range in the output of the transmitter-amplifier 2.

` The devices 9 and 10 constitute a novel arrangement for controlling the operation Vof the s stem. The compressor 9 has a range ot .60 T which, as. will be noted, is the range of volume inthe output of the transmitteramplifier, namely from 15 TU to -45 TU.' Theefect-of this compressor is to reduce the volume ,as indicated by the indicator 10 to -45'TU. lA's'- will be clearly seen in Fig. 2,

- the Icontact points or brushes of the potenztiolneters constituting the compressors 3 and 9 are so connected .that the movement of one of the contactfpoints produces a corresponding movement of the contact point of the other. Accordingly, when the operator at the control station moves the arm of the 'compressor 9 so as to keep the reading of the volumel indicator-10 constant at a level of TU, such movement-of thearm will produce a. corresponding movement of the contact point of the compressor 3, thereby insurof the amplifier 4Will range between 30 .TU

i and -45 TU.

- The manner` in which the various devices at the sending and the receiving ends of the line L1 are inter-controlled is shown clearly in Fig. 2, in which the same numerals have been used to indicate similar parts, The conductor '.11 of the output circuit of the transmitter-amplier 2 is connected with one of the terminals of the potentiometer desig nated compressor 3, and conductor 12 is connected 'with the other terminal of this potentiometer winding, the connection including a fixed resistance 13. In like manner, the con-Q ductor 11 is also connected with the Windingl of the potentiometer designated compressor.

9, and conductor 12 is connected with the other terminal of this winding, the connection including a xed resistance 14. -The contact points of these potentiometer windings, which are represented by brushes, are' carried by a single control arm 15, but are.

insulated each from the other. Thus the brush 16 ofthe compressor?) is connected by conductor 17 with the grid of the amplifier 4.

The brush 18 of the compressor 9 is connected by 'conductor 19 With one terminalof the volume indicator 10, the other terminal of which iseffectively connected with conductor 12. The other end ofthe arm 15 carries a brush 2O which moves along thevvinding 21 so as to effectively bridge portions of this Winding, Which is a resistance element, across theline Lmvvvhich connects the generator 22 with the control apparatus at the distant stations. This line may have therein one or more repeaters such as 23. The line Ll is con,-l nected directly with the station No. 1, that is to say, Without the interposition. of any expanding device. .Bridged across the line L2 at the points 24and 25 are the expanders designated A, B and C. Expander A in cludesa relatively large lixed resistance 26 in series with a variable element of lower resistance 27. Similarly,`expanders B and C comprise xed resistances 2S and 29, re#

spectively, 29 being smaller than 28, and va riable resistances 30 and 31, respectively, the resistance 30 beiner less than 3l. A plurality of solenoids, 32, 33 and 34,' are effectively bridged across the line L2 and control thev of 60 TU comprised between the levels oi" +15 TU and -45 TU, the operator at the transmitting station will operato' the arm 15" of the potentiometer control system in order to keep Vthe reading of the volume indicator substantially constant at'the 45 point upon the scale. In doing' this, the operator also effects the movement of the brush 16 upon the winding of the compressor 3 so as to fix the volume, that Willbe applied to the -amplifier 4, between the limits ot the -30 TU and the -45 TU. If the volume of the transmitter l output would indicate an upward trend by the device 10, the operator would make such` adjustment as tovlower the volume range, and in s ol doing, he would not only control the limit applied to the input of the. amplifier 4, butl would also effect an adjustment of the variable resistance 21, which is shunted.

across the line L2. This controls the power supplied to the solenoids 32to 34 at the stations at the distant end of the line L2, and the arms 35, 36 and 37 of the expanders A, B and C will take a position depending upon the strength of the` current owing throughr the, -sole noids, which ldepends upon the"'setting of the brush 20 upon the resistance 21 at the sending station. The volume range applied to theampliiers 38,39A and 40 will thereby be controlled. Thus, if the volume at the out- .put ofthe ampliier 2 is' reduced by the'compressor, it is automatically increased at each ofthe stations'Nos. 2, 3 and 4, and vice versa, if the volume is increased at the sending sta.-A tion, so as to bring it within the range intended for the line L1, it will be reduced by l the expanders A, B and C, which will be controled by the current sent over the line L2 from the generator 22.

It is desirable to mention that while the stations 1 to 4, inclusive, seem to be connected with the line'L1 at the same point, such arrangement has been made to render the drawing more compact. However, as statedin .connection with Fig. l, the broadcasting stations and the loud speaker system may be connected with'the line at different points throughout its length.,

It is to be understood,- of course, that the arrangement shown in Fig. 2 may be varied in its details in many ways that will suggest ,themselves to persons skilled in the art.

' Thus, in place of a generator such Vas 22, whose output current is controlled bythe shunting device -21, it is possible to use a step-bystep method of control to effect the operation shown.

volume. range of an electrical transmission system comprising a plurality of receiving stations, a transmitting station commento the receiving stations, and a wire line connecting the said transmitting station with all of the receiving'stations, the method which consists in compressing the rangelof volume of power at the transmitting station to bring it within the range that the wire line is capable of efficiently handling, and expanding the volume range at each of the said receiving stations to different degrees, the degree of I expansion at each station depending upon I j the requirements of the particular station.

4 2. In an arrangement for controlling the volume range of an electrical vtransmission system, the combination with a transmitting medium of a source capable of producinga volume of power having a widerange between its upper and lower levels, a volume range compressor and an amplier connected in sequence between the said source and the said transmitting medium, the said compressor being adjusted to compress the volume range of the said source to the degree neces-l sary to bring it within the volume range that the said medium is capable of transmitting, and the said amplifier being adjusted to control the levels of the said volume without changing the range of the said volume for transmission over the said medium, a volume indicator anda second compressor connected between the said indicator and the said source,

the said compressors being so connected that the adjustment of the second compressor to keep the reading ofthe volume indicator at a predetermined point, automatically adjusts the-first compressor to keep the levels at such points as to compress the volume range produced by said source to the range that the said transmitting medium is capableof transmittin 3g. In an arrangement for controlling the volume range of an electrical transmission system` comprising a plurality of receiving stations, a transmitting station common to the receiving stations, and a wire line connecting the said transmitting station to all of the receiving stations, the methodwhich consists in compressing the range of volume at the,`

transmitting station to bring it Within the range that the wireline is capable of efficiently handling, varyin the level of the volume as thus compresse range, transmitting the said volume and expanding the .volume range at each of the reeol without changing its ceiving stations to different degrees, the dey gree ofexpansion at each station depending upon the requirements of the particular station.

' In testimony whereof, we have signed our names to this specification this 18th day of December, 1925.

oscAR B. HANsoN. eEoRGEcRIssoN.

FREDERICK w. MirowN. 

